新型鸭肝炎病毒流行病学调查及免疫防治试验

Epidemiological investigation and experimental immunization of Non-serotype 1 duck hepatitis virus

本试验通过鸭胚尿囊腔接种,对我国部分省市采集的死于疑似鸭病毒性肝炎的病鸭肝组织进行病原分离,获得9个病毒分离株。这些分离株对10日龄鸭胚的致死率为100%,人工感染6日龄雏鸭的致死率为0~100%不等。死亡鸭呈角弓反张姿势,剖检可见肝脏肿大,有出血点或出血斑。将9株分离株经鸭胚传至第5代,收集鸭胚尿囊液毒测定这些毒株的ELD50为10-7.32/0.2 ml^10-3.5/0.2 ml不等。用鸡抗1型DHV及新型DHV的血清进行中和试验,结果表明:有7株为新型DHV,有2株为1型DHV。对实验室早期分离的新型鸭肝炎病毒B株经过鸭胚传代致弱后,收集鸭胚尿囊液毒稀释成不同倍数对1日龄雏鸭进行免疫,并于10日龄时用新型鸭肝炎强毒进行攻毒保护试验,结果B20株在20倍稀释时,保护率达100%。采集免疫的雏鸭血清,中和试验测定血清的效价,雏鸭在免疫后可检测到中和抗体,第10天时抗体水平达到高峰,然后呈逐渐下降趋势。结果表明,B株经过鸭胚传代致弱后在毒力下降的同时仍保留一定的免疫原性,可以作为疫苗的候选株。

Nine strains of duck hepatitis virus （DHV） were obtained from duckling liver samples through duck embryo by allantoic sac inoculation. All these samples were collected from ducklings diagnosed clinically dying from duck virus hepatitis in several provinces of China. The lethal rate of 10 day-old duck embryos inoculated with these isolates was 100 percent. When inoculating 6 day-old ducklings with these isolates, the mortality rate was among 0--100%. Dead ducklings showed the sign of opisthotonus,with swollen and punctuate hemorrhage in their livers. The ELD50 of these virus strains determined with duck embryos were among 10.7.32- 10 35 Viral neutralization test was done using standard sera against DHV type 1 and non-serotype 1 DHV. Seven of nine isolates belonged to nonserotype 1 DHV, the other two belonged to DHV type 1. A strain of non-serotype 1 DHV previously isolated from Beijing was attenuated by passage in duck embryos and designated B20strain. Diluted allantotic fluid virus was used to immunize 1-day-old ducklings and the immunized ducklings were challenged with virulent non-serotype 1 10 days post immunization. The result indicated that the protection rate of 20 folds dilution of B20could reach up to 100 percent. However, 100-fold dilution of B20 provided no protective effect. The sera of the immunized ducklings were collected and the antibody titers were measured by virus neutralization test. The antibody level reached peak in l0 days post vaccination and then decreased. The results showed that B20 strain could provide protection against the infection with non-serotype 1 DHV and may be used as the candidate vaccine strain.